There's console feature called store (ESC[8]). Well, it is reallyusefull (for example if you want your machine to be green becausemonitor has problems with convergence). However, after that, evenconsole reset does not set values back. Try this on your favouritepublicly-accessible linux and enjoy.

echo -e '\33[30m\33[8]'; logout

Cure is (of course) simple: log in and type echo -e '\33[32m', forexample. But I doubt you'll figure this out when you see black screen.